1. Field of the Invention
The present invention relates to a biological information imaging apparatus and a method for analyzing biological information.
2. Description of the Related Art
Imaging apparatuses using X-ray (mammography), ultrasound or MRI (magnetic resonance imaging) have been often used for diagnosing breast cancer.
In recent years, a photoacoustic imaging apparatus has been noted, in which the imaging apparatus propagates pulsed light from a light source such as a laser into a living body, detects a photoacoustic signal generated by absorption of the propagated light into the living body, and images an initial pressure distribution or absorption coefficient distribution in the living body. This technique is referred to as PAT (PhotoAcoustic Tomography).
Generally, photoacoustic tomography has the following advantages. First, photoacoustic tomography can perform functional imaging of oxygen metabolism and brain activity without having to perform imaging of a living body using X-rays, ultrasound or MRI.
For example, oxy-hemoglobin and deoxy-hemoglobin have different optical absorption spectrums. Thus, a plurality of wavelengths can be used to measure the absorption spectrums to measure oxygen saturation in blood and oxygen metabolism.
The imaging of oxygen metabolism advantageously enables examination of cancerous tumors, or of active areas in the brain.
Imaging of oxygen metabolism also enables identification of the composition of a diseased part from the absorption spectra.
Second, light does not involve radiation exposure unlike X-rays or radiation such as gamma-rays, and enables repeated non-invasive diagnosis.
Third, medical devices can be reduced in size and cost as compared with MRI and PET (positron emission tomography) apparatus.
As compared with an optical diffusion imaging apparatus also capable of functional imaging that detects diffused light and images the inside of a living body, lower scattering of photoacoustic waves occurs in the living body, which thus enables an increase in resolution.
In recent years, Japanese Patent Application Laid-open No. 2005-021380 proposes an apparatus including a combination of an ultrasound diagnostic apparatus and a photoacoustic imaging apparatus for using both an ultrasound echo image and a photoacoustic image for diagnosis.
In this apparatus, by the combination of the apparatuses and partial sharing of systems, both of the photographed images can be displayed without distortion.
In the general photoacoustic imaging apparatus, strong optical diffusion in the subject living body causes a significant reduction in light intensity as the light penetrates into deeper parts of the living body. Specifically, in the deep parts of the living body, the number of photons reaching the optical absorber is significantly decreasing.
Thus, a photoacoustic signal that can be observed by a sound wave detector placed on a surface of the living body cannot be obtained from the deep part of the subject, and the region in the living body that can be imaged is limited.
Such a problem is not disclosed in the combination of the ultrasound apparatus and the photoacoustic imaging apparatus in Japanese Patent Application Laid-open No. 2005-021380.